Vinyl chloride resins are widely used in the manufacture of various useful end products, including moldings, tile, pipe, sheets, film, bottles, and the like. Unfortunately, unplasticized vinyl chloride resins used in the manufacture of rigid end products tend to have poor heat deformation characteristics. Consequently, they are unsuitable for use in certain areas of application where structural integrity under heat and load is of prime importance.
Heretofore, attempts have been made to improve upon the relatively poor heat deformation characteristics of polyvinyl chloride resins. For example, in U.S. Pat. No. 3,626,033 ternary compositions are described which comprise 50 to 75 weight percent of a vinyl chloride resin, 10 to 35 weight percent of a polydiene rubber nitrile graft copolymer and 15 to 35 weight percent of an anhydride-containing copolymer, such as styrene-maleic anhydride.
British Pat. No. 1,297,505 discloses that small amounts of certain copolymers such as styrene-maleic anhydride can be admixed with polyvinyl chloride homopolymer to improve impact strength of the end product. The amount of such anhydride copolymer used ranges from 0.1 up to 5 parts by weight per 100 parts by weight of the PVC homopolymer. Although tensile impact strength of the PVC is shown to be improved by this means, nothing is said about the heat deformation characteristics of the resultant binary blends.
In Journal of Applied Polymer Science, Vol. 21, pages 791-796 (1977), the results of torsional pendulum analyses are set forth for a 50:50 blend of polyvinyl chloride and styrene-maleic anhydride copolymer. At page 795 the authors points out that this blend is opaque and brittle, bearing all the marks of incompatability . The styrene-maleic anhydride copolymer used in this experimental work was Dylark 232 from ARCO/Polymers, Inc. which is understood to contain 92 percent by weight of styrene and 8 percent by weight of maleic anhydride. It is rubber free.